The invention relates to the manufacture, remanufacture, and restoration of nickel- or cobalt-based superalloy parts. More particularly, the invention relates to the restoration and/or remanufacture of defective, worn, and/or damaged gas turbine engine components including turbine and compressor blades and vanes, blade outer air seals, and transition duct segments.
The components of gas turbine engines are subject to wear and damage. Even moderate wear and damage of certain components may interfere with optimal operation of the engine. Particular areas of concern involve parts which interact with the gas path such as seals and the airfoils of various blades and vanes. Wear and damage may interfere with their aerodynamic efficiency, produce dynamic force imbalances, and even structurally compromise the worn/damaged parts in more extreme cases.
Various techniques have been proposed for more extensive restoration of worn or damaged parts of gas turbine engines. U.S. Pat. No. 4,822,248 discloses use of a plasma torch to deposit nickel- or cobalt-based superalloy material. U.S. Pat. No. 5,732,467 identifies the use of high velocity oxy-fuel (HVOF) and low pressure plasma spray (LPPS) techniques for repairing cracks in such turbine elements. U.S. Pat. No. 5,783,318 also identifies LPPS techniques in addition to laser welding and plasma transferred arc welding. U.S. Pat. No. 6,049,978 identifies further use of HVOF techniques. Such techniques have offered a limited ability to build up replacement material to restore an original or near original cross-section. However, the structural properties of the replacement material may be substantially limited relative to those of the base material. U.S. Pat. Nos. 4,008,844 and 6,503,349 disclose methods and repair materials for transient liquid phase diffusion brazing repairs. Such a repair material is available under the trademark TURBOFIX.
Cracks tend to be rather narrow (e.g., 0.25 mm or less), but can be much wider depending upon engine exposure and oxidation. For thin cracks, it may be advantageous to form a diffusion bond crack repair (i.e., without machining out the crack to broaden the crack). This is also identified as “healing” the crack in a metallic substrate. An advantage of a healing is that the small transverse distances across the crack permit substantial diffusion, allowing the melting point depressants to diffuse out from the material within the crack and leaving highly near base metal composition. For typical nickel-base superalloys this results in an isothermally solidified structure whose mechanical properties are near that of the base metal.
For larger defects (e.g. large chips, wear areas, or contaminated cracks requiring routing out to provide a clean base metal surface) a “build-up” repair is required (e.g., wherein portions of the repair material are more than about 1 mm from the nearest base metal of the substrate). In many cases, a common alloy mixture may be used for both crack and build-up repairs although specifically designed “preforms” (i.e., prostheses) may be developed for a recurrent build-up repair. For build-up repairs, usually only a partial isothermal structure is achieved due to limitations in diffusion time relative to the required diffusion distances. As such, the build-up repair will have a coarse, more globular, type of microstructure while the crack repair will tend to look much like the base alloy with a defined grain structure.
For parts having cooling passageways, various techniques have been proposed for preserving those passageways when the passageways intersect the damage or wear site. U.S. Pat. No. 6,742,698 discloses a refractory metal insert used with welding repairs along a trailing edge region of an airfoil. U.S. Pat. No. 5,935,718 discloses inserts used in brazing and solder repairs.